Switching regulators, including ripple regulators, are commonly used because of their characteristic of high efficiency and high power density resulting from smaller magnetic, capacitive, and heat sink components. In current-mode control, for example, switching regulators indirectly regulate an average DC output voltage by selectively storing energy by switching energy on and off in an inductor. By comparing the output voltage to a reference voltage, the inductor current is controlled to provide the desired output voltage.
Synchronous buck power stages are a specific type of switching regulator that use two power switches such as power MOSFET transistors. A high-side switch selectively couples the inductor to a positive power supply while a low-side switch selectively couples the inductor to ground reference. A pulse width modulation (PWM) control circuit is used to control the high-side and low-side switches. Synchronous buck regulators provide high efficiency when low on-resistance power MOSFET devices are used.
With increased demand for low voltage power, the synchronous rectifier (SR) is an important circuit element in the DC-DC converter mainstream. One such use of the synchronous rectifier is the low-side switch in buck power stages.
The added emphasis on synchronous rectification is also posing design problems for the DC-DC converter designer. Typical SR design considerations include gate timing control, gate driver, and reverse conduction. For example, significant power losses can result from the delay necessary for switching on states between the high side and low side to prevent the simultaneous conduction of the high-side and the low-side switches. To maximize power efficiency, it is desirable to minimize the delay times to an optimal level, while preventing simultaneous cross-conduction of the high-side and low-side switches and output error.